Process for the preparation of chrome-leather.



FIQ'E.

ALBERT WOLFE, OF COLOGNE, GERMANY.

PROCESS FOR THE PREPARATION OF CHROME-LEATHER.

No Drawing.

To all whom, it may concern:

Be it known that I, ALBERT WoLrF, a subject of the Emperor of Germany, and residing at Cologne-on-the-Rhine, in the Kingdom of Prussia and Empire of Germany, have invented certain new and useful Improvements in Processes for the Preparation of Chrome-Leather of which the following is a specification.

For tanning hides certain salts of chromium, especialy chrome alum have been used for a long time. I have found, that solutions of chromium formate which is easily soluble in water are more suited for tanning hides than all the other salts of chromium hitherto employed. The advantage in using solutions of chromium formate consists in the thorough tanning of the hides taking place much quicker than by the old method. Furthermore no addition of alkali is required during the tanning process. The chromium leather obtained possesses uniform and excellent properties and is of great tensile strength.

For carrying out the tanning process a solution of pure chromium formate is employed preferably made by the double decomposition of a concentrated solution of chromium sulfate with solid sodium formate whereupon the sodium sulfate formed and precipitated is separated from the solution by means of a centrifugal machine. The product of reaction which is formed by stirring solid sodium formate with a concentrated solution of chromium sulfate can also directly be employed for that purpose after diluting the product of reaction with water, the presence of sodium sulfate being no hindrance. Both a neutral or a basic solution of chromium sulfate can be used for the preparation of chromium formate.

Compared with the old methods the present process is characterized by no mineral acid being liberated during the tanning process but only formic acid.

Specification of Letters Patent.

Application filed. October 24, 1911.

Patented Apr. 16, 1912.

Serial No. 656,387.

In the British Patent 14293/1896 a chromium tanning solution is mentioned in which sodium formate is present. According to that patent the tanning process is practically carried out with a solution of chromium sulfate or chromium chlorid because the amount of formate present can only combine with less than one fifth of the chromium, even if a decomposition between the chromium and the formate would take place in the diluted state, which according to my experience is not the case.

Example I: The cleaned and pickled skins freed from hair are treated with a tanning solution made from pure chromium formate in the tanning tub for some hours. The solution should have a strength of about 1.07 to 1.085 spec. grav. The further treat ment of the leather tanned in this manner is the customary one as applied for chrome leather.

Example II: To 100 parts of a chromium sulfate solution containing 15% of chromium oXid are added 42 parts of solid sodium formate or to 100 parts of basic chromium sulfate solution are added 28 parts of solid sodium formate the mixture being well agitated. After standing for two hours the product of reaction is diluted. with five or ten times the quantity of water. The skins are then treated with that tanning solution.

What I claim is A process for the preparation of chrome leather consisting in treating cleaned and pickled skins freed from hair with an aqueous solution of substantially pure chromium formate.

In testimony whereof I affix my signature in presence of two witnesses.

ALBERT WOLFF.

Witnesses HENRY HASPER, WOLDEMAR HAUPT.

Copies of this patent may be obtained for five cents each, by addressing the Commissioner of Patents,

- Washington, I). G. 

